Optical disk, tracking error signal generating apparatus, and tracking control apparatus

ABSTRACT

An optical disk includes: a plurality of recording tracks, each of the recording tracks having a data area for storing data, and a servo control information area for storing servo information; and tracking pits respectively formed on n neighboring recording tracks, which are adjacent to each other in a radial direction of the optical disk, where n is an integer not less than 3. The tracking pits are located in the servo control information area of each of the n neighboring recording tracks and are spaced apart from each other by a distance not less than a radius of a beam spot for reading data from the optical disk. The tracking pits of the n neighboring recording tracks are located on different radial lines of the optical disk.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical disk, a tracking errorsignal generating apparatus, and a tracking control apparatus. Moreparticularly, the present invention is concerned with ahigh-recording-density optical disk using a sampled servo method, atracking error signal generating apparatus for generating a trackingerror signal from such an optical disk, and a tracking control apparatusfor performing tracking control of such an optical disk.

2. Description of the Related Art

There is a recording format based on a sampled servo method as arecording format of an optical disk.

FIG. 1 shows a recording format of an optical disk of the sampled servomethod. The optical disk based on the sampled servo method does not haveany pre-grooves (guide grooves) on a recording film of the optical disk,but servo areas (fields) at 1376 points in one track are pre-formatted.The optical disk based on the sampled servo method is characterized inthat a tracking error and a clock for recording/reproducing can begenerated by sampling by means of the pre-format.

As shown in FIG. 1, a signal track having a spiral form extending fromthe inner portion of an optical disk DK to the outer portion thereof isformed in a program area PA of the optical disk DK. One track is dividedinto 32 sectors. Each of the sectors includes 43 segments, and each ofthe segments contains 18 bytes. In the first segment #0 of one sectorare pre-formatted a sector synchronizing signal S_(sync) (two bits) forestablishing synchronization for each sector and a sector addressS_(ADR) (16 bits) for indicating the address of the above sector. Theabove pre-formatting is performed in the process of mastering of theoptical disk. Each of the segments #1 to #42 consists of a 18-byte areaincluding a two-byte servo area F_(S) and a 16-byte data area F_(D).

FIG. 2 shows a recording format o the servo area F_(S). The two-byteservo area F_(S) is segmented into two servo bytes #1 and #2. A firstwobble pit P_(W1) is pre-formatted at the third bit of the servo byte#1, and a second wobble pit P_(W2) is pre-formatted at the eight bitthereof. As shown in FIG. 2, the position of the first wobble pit P_(W1)is located at the third bit in 16 tracks (A), and is indicated asP_(W1A). The position of the first wobble pit P_(W1) is located at thefourth bit in 16 tracks (B), and is indicated as P_(1B). In this manner,since the position of the first wobble pit P_(W1) is changed every 16tracks, the number of tracks crossing during searching can be correctlydetected.

The first wobble pit P_(W1) and the second wobble pit P_(W2) aredisposed so that these pits are respectively shifted, by 1/4 of thetrack pitch, from a track center TC in a direction (the radial directionof the writable optical disk DK) perpendicular to the trackingdirection. A tracking error detection is performed on the basis of thedifference between the quantity of a return light obtained at the firstwobble pit P_(W1) and the quantity of a return light obtained at thesecond wobble pit P_(W2). A clock pit CP for synchronization ispre-formatted at the 12th bit in the servo byte #2. A space between thesecond wobble pit P_(w2) and the clock pit CP has a mirror surface andhas a clock length equal to 19 channels. Synchronization can beestablished for each segment by counting this 19 channel clockpre-formatted in the above space. Focus error detection is also carriedout during the synchronization detection period. FIG. 2 shows a signalS_(T1) (S_(T1A) or S_(T1B)) for use in tracking and the sectorsynchronizing signal S_(sync), these signals being obtained by readingthe servo area F_(S) by the laser beam.

A description will now be given, with reference to FIG. 3, of a methodfor detecting a tracking error by means of wobble pits. A reference Aindicates a first case where the read beam runs on the center axis(track center axis) between a pair of wobble pits P_(W1) and P_(w2). AnRF signal obtained in the first case is indicated as S_(A). When theread beam runs near the wobble pit P_(W1) or P_(W2), a small quantity ofreflected light is obtained due to the optical diffraction effect, andthe reflected light becomes dark. When the read beam passes just on theclock pit CP, the darkest reflected light is obtained. A reference Bindicates a second case where the read beam moves on a portion deviatingfrom the track center axis towards the inner circle end of the opticaldisk. The RF signal obtained in the second case is indicated as S_(B).In the second case, since the read beam passes just on the wobble pitP_(W1), the dark portion by the wobble pit P_(W1) is darker than that bythe wobble pit P_(W2). A reference C indicates a third case where theread beam moves on a portion deviating from the track center axistowards the outer circle end of the optical disk. The RF signal obtainedin the third case is indicated as S_(C). The RF signal S_(C) has awaveform reverse to that of the RF signal S_(B).

It is assumed that SAMPLE (T₁) indicates a signal value obtained byperforming signal sampling at the time of the wobble pit P_(W1), andSAMPLE(T₂) indicates a signal value obtained by performing signalsampling at the time of the wobble pit P_(W2). The difference betweenthe SAMPLE(T₁) and the SAMPLE(T₂), that is, SAMPLE(T₁)-SAMPLE(T₂) isequal to zero, a negative value and a position value in the first,second and third cases A, B and C, respectively. Assuming thatSAMPLE(T₁)-SAMPLE(T₂)=Te, the TE can be used as a tracking error signal.

In the above-mentioned conventional sample servo method, the wobble pitsP_(W1) and P_(W2) as well as the clock pit CP are per-formed on theoptical disk (pre-pits), and a variety of information for use in servocontrol, such as a tracking error signal, is generated by thearrangement of these pits.

In the information reading operation, the laser beam reflected by thesignal pit PT is also diffracted by the signal pit PT, and a smallquantity of light returns to the optical pickup therefrom, so that theposition of the signal pit PT is handled as a dark portion. On the otherhand, the space between the signal pits PT has a mirror surface, and thelaser beam is totally reflected by the mirror surface. Hence a largequantity of light returns to the optical pickup, and the correspondingportion is handled as a light portion. In order to correctly read servoinformation, it is necessary to read the above darkness and lightnesswithout any error. In order to read darkness and lightness withouterror, conventionally, as shown in FIG. 4A, it is necessary to design atrack pitch width T_(P) (approximately 1.6 μm, for example) so that itis greater than the diameter B_(L) of a spot format by the laser beam.

In the above case, in order to improve the recording density of theoptical disk DK, it may be considered to reduce the track pitch width.FIG. 4B or FIG. 4C shows the track pitch width T_(P) reduced to a half(approximately 0.8 μm) of the conventional width. The difference becomessmall between the quantity of light obtained in an on-track state shownin FIG. 4B, in which the center of the laser beam is located on thetrack center axis, and the quantity of light obtained in an off-trackstate shown in FIG. 4C, in which the center of the laser beam is locatedout of the track center axis, and hence the servo control cannot becorrectly performed. As a result, it is impossible to reduce the trackpitch width beyond a limited value. It may be considered to shorten thewavelength of the laser beam and diminish the size of the pits in orderto improve the recording density of the optical disk DK. However, alsoin this case, there is a limit regarding the track pitch due to the spotdiameter B_(L). Further, it become difficult to record the wobble pitsat high speed and high precision.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an optical disk, atracking error signal generating apparatus and a tracking controlapparatus, in which the tracking error signal can be easily generated ina state in which the track pitch becomes narrower than the diameter of aspot formed by a read laser beam, and tracking control can be easilyperformed, so that the recording density can be improved withouthigh-precision wobble pits.

According to the present invention, the above mentioned object can beachieved by an optical disk including: a plurality of recording tracks,each of the recording tracks having a data area for storing data, and aservo control information area for storing servo information; andtracking pits respectively formed on n neighboring recording tracks,which are adjacent to each other in a radial direction of the opticaldisk, where n is an integer not less than 3. The tracking pits arelocated in the servo control information area of each of the nneighboring recording tracks and are spaced apart from each other by adistance not less than a radius of a beam spot for reading data from theoptical disk. The tracking pits of the n neighboring recording tracksare located on different radial lines of the optical disk.

According to the present invention, the above object can be alsoachieved by a tracking error signal generating apparatus in an opticaldisc player, which generates main read beam for reading data recorded onone of tracks formed on the above described optical disk of the presentinvention, and two sub read beams for reading data recorded on twotracks adjacent to one of the tracks. The tracking error signalgenerating apparatus includes: a timing generating device for generatinga plurality of sampling timings respectively corresponding to recordingpositions of the tracking pits for the main read beam and the two subread beams; a sample and hold device for sampling reproduced signalsrespectively corresponding to the main read beam and the two sub readbeams on the basis of the plurality of sampling timings and for holdingthe sampled reproduced signals; a comparing device for comparing levelsof the sampled reproduced signals respectively corresponding to theplurality of sampling timings and for outputting a selecting signalindicating one of the sampling timings at which one of the sampledreproduced signals has a largest level; a selecting device forselectively outputting, from the sample and hold device, the sampledreproduced signals obtained from the two sub read beams at one of thesampling timings indicated by the selecting signal; and an operationdevice for outputting a tracking error signal on the basis of thesampled reproduced signals from the selecting device.

According to the present invention, the above mentioned object can bealso achieved by a tracking control apparatus having the above describedtracking error signal generating apparatus of the present invention, inan optical disc player, which generates main read beam for reading datarecorded on one of tracks formed on the optical disk of the presentinvention, and two sub read beams for reading data recorded on twotracks adjacent to one of the tracks. The tracking control apparatusincludes: a signal generating device for generating a pull-in trackingerror signal from read signals of the tracking pits read by the two subread beams at one of the sampling timings; and a pull-in device forpulling the main read beam in one of the recording tracks on the basisof the pull-in tracking error signal.

According to the present invention, the above mentioned object can bealso achieved by another tracking control apparatus having the abovedescribed tracking error signal generating apparatus of the presentinvention, in an optical disc player, which generates main read beam forreading data recorded on one of tracks formed on the above describedoptical disk of the present invention, and two sub read beams forreading data recorded on two tracks adjacent to one of the tracks. Thetracking control apparatus includes: a signal generating device forcomparing levels of read signals of the main read beam, at respectiveread timings of the tracking pits formed on the adjacent recordingtracks, with each other, selecting the read timing at which the level ofread signal is larger, and generating a pull-in tracking error signalfrom the read signals of the two sub read beams at the selected readtiming; and a pull-in device for pulling the main read beam in one ofthe recording tracks on the basis of the pull-in tracking error signal.

According to the present invention, the above mentioned object can bealso achieved by another tracking error signal generating apparatus forgenerating a tracking error signal from read signals from the abovedescribed optical disk of the present invention. The tracking errorsignal generating apparatus includes: a read device for outputting readsignals at a plurality of read timings corresponding to recordingpositions of the tracking pits by reading a recording track of interestby means of a read beam; a comparing device for comparing levels of theread signals respectively obtained at the read timings and for selectingone of the plurality of read timings at which one of the read signalshas a largest level; and an operation device for selecting read timingsat which the tracking pits formed on the recording tracks adjacent tothe recording track of interest are read on the basis of the selectedread timings selected by the comparing device and for generating thetracking error signal on the basis of the read signals corresponding tothe selected read timings.

According to the present invention, the above mentioned object can bealso achieved by another tracking control apparatus for performingtracking control of the above described optical disk of the presentinvention. The tracking control apparatus includes: a signal generatingdevice for generating a tracking error signal on the basis of a readsignal output by reading by means of a read beam at fixed one of readtimings at the time of counting recording tracks; and a count device forcounting a number of tracks by a unit of cycle of recording positions ofthe tracking pits on the basis of the tracking error signal.

According to one aspect of the present invention, tracking pits arerespectively formed on n recording tracks adjacent to each other in aradial direction of an optical disk, where n is an integer equal to orgreater than 3. The tracking pits are located in a servo controlinformation area of each of the n recording tracks and are spaced apartfrom each other by a distance equal to at least a radius of a beam spotfor reading data from the optical disk. The tracking pits are located ondifferent radial lines of the optical disk. Hence, in tracking control,there is no interference of waveforms from adjacent recording tracks,and there is no need to provide wobble pits. Hence it becomes possibleto perform tracking control of a fine track pitch and increase therecording density.

According to another aspect of the present invention, timing generatingmeans generates a plurality of sampling timings respectivelycorresponding to recording positions of the tracking pits for the mainread beam and the two sub read beams. Sample and hold means samplesreproduced signals respectively corresponding to the main read beam andthe two sub read beams on the basis of the plurality of sampling timingsand holds sampled reproduced signals. Comparing means compares levels ofthe sampled reproduced signals respectively corresponding to theplurality of sampling timings and generates a selecting signal foroutputting a selecting signal indicating one of the sampling timings atwhich one of the sampled reproduced signals having a largest level isobtained. Selecting means selectively outputs, from the sample and holdmeans, the sampled reproduced signals obtained from the two sub readbeams at the one of the sampling timings indicated by the selectingsignal. Operation means outputs the tracking error signal on the basisof the sampled reproduced signals selectively output by the selectingmeans. Hence, it is possible to record information with a high recordingdensity and to easily and certainly generate the tracking error signaleven when the tracking pitch is narrow.

Yet another aspect of the present invention, pull-in means generates apull-in tracking error signal from read signals of the tracking pitsread by the two sub read beams at one of the sampling timings and pullsthe main read beam in one of the recording tracks on the basis of thepull-in tracking error signal. Hence, it is also possible to increasethe controllable pull-in range using the tracking error signal even fora reduced track pitch and to stably pull the read beam in a track.

A further aspect of the present invention, pull-in means compares levelsof read signals obtained by reading the tracking pits formed on the twoadjacent recording tracks at respective read timings with each other,generates a pull-in tracking error signal from the read signals, andpulls the main read beam in one of the recording tracks on the basis ofthe pull-in tracking error signal. Hence, it is also possible toincrease the controllable pull-in range using the tracking error signaleven for a reduced track pitch and to stably pull the read beam in atrack.

A still further aspect of the present invention, read means outputs theread signals at a plurality of read timings corresponding to recordingpositions of the tracking pits by reading a recording track of interestby means of a read beam. Comparing means compares levels of the readsignals respectively obtained at the read timings and selects one of theplurality of read timings at which one of the read signals having alargest level. Operation means selects the read timings at which thetracking pits formed on the recording tracks adjacent to the recordingtrack of interest are read at selected read timings, and generates thetracking error signal on the basis of the read signals corresponding tothe selected read timings. Hence, it is possible to record informationwith a high recording density and to easily and certainly generate thetracking error signal even when the tracking pitch is narrow.

Furthermore, according to the present invention, count means generates atracking error signal on the basis of a read signal output by reading bymeans of a read beam at a fixed one of read timings at the time ofcounting recording tracks, and counts a number of tracks with a periodof recording positions of the tracking pits on the basis of the trackingerror signal. Hence, it is possible to count the number of recordingtracks even when recording tracks are crossed.

The nature, utility, and further features of this invention will be moreclearly apparent from the following detailed description with respect topreferred embodiments of the invention when read in conjunction with theaccompanying drawings briefly described below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a recording format of a sampled servomethod;

FIG. 2 is a diagram of a recording format of a conventional servo area;

FIG. 3 is a waveform diagram illustrating detection of a tracking errorby means of conventional wobble pits;

FIGS. 4A, 4B and 4C are respectively diagrams illustrating disadvantagesof the conventional art;

FIG. 5 is a diagram of a recording format of an optical disk;

FIG. 6 is a diagram of a positional relationship between read beams;

FIG. 7 is a block diagram of an essential part of a reproducingapparatus according to a first embodiment of the present invention;

FIG. 8 is a block diagram of a detailed structure of a sample and holdcircuit;

FIGS. 9A and 9B are diagrams showing the operation of the firstembodiment of the present invention;

FIGS. 10A and 10B are diagrams showing the operation of the firstembodiment of the present invention;

FIG. 11 is a waveform diagram of a tracking error signal;

FIG. 12 is a block diagram of an essential part of a reproducingapparatus according to a second embodiment of the resent invention;

FIG. 13 is a block diagram of an essential part of a reproducingapparatus according to a third embodiment of the present invention;

FIGS. 14A, 14B, 14C, 14D and 14E are respectively diagrams showing theoperation of the third embodiment of the present invention; and

FIG. 15 is a diagram of a timing selecting table.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will now be given of preferred embodiments of the presentinvention.

First Embodiment

FIG. 5 shows a recording format of an optical disk according to a firstembodiment of the present invention. In the following description, agroup of four neighboring recording tracks defines a cycle of therecording positions of tracking pits.

FIG. 5 shows a part of the optical disk, and more particularly showsrecording track groups TG_(n-1), TG_(n), TG_(n+1) and TG_(n+2), eachgroup consisting of four neighboring recording tracks. The followingdescription mainly relates to the recording track group TG_(n).

Each of recording tracks TR₁ to TR₄ (track numbers TNO=1 to 4) formingthe recording track group TG_(n) is provided with a tracking pit areaATR, a sync (SYNC) area ASY and a clock pit area ACR arranged in thisorder from the head of the arrow indicating the disk rotating direction(upper side of the drawing). A data area (not shown) used to record avariety of data is provided on the lower side of the drawing.

The tracking pit area ATR has four tracking pits respectively located atdifferent positions (i.e. on different radial lines) on the recordingtracks TR₁ to TR₄.

In the clock pit area ACR, clock pits CP are respectively provided forthe recording tracks TR₁ to TR₄ so that the clock pits CP are arrangedin a line in the radial direction of the optical disk (i.e. on a sameradial line). The clock pits CP indicate the clock generating timing.

More concretely, the recording track TR₁ is provided with a tracking pitTP₁ located at a position corresponding to the center of a read beamLB_(B) obtained prior, by time T₁ (sampling timing), to a reference timeat which the clock pit CP is read by the read beam LB_(B) (or a readbeam LB_(A) or a read beam LB_(C)) while the optical disk is beingrotated at a regular velocity.

The recording track TR₂ is provided with a tracking pit TP₂ located at aposition which is further away from the center of the tracking pit TP₁by a distance L in the circular direction (i.e. disk rotating direction)of the optical disk DK. The sampling timing is time T₂ at the aboveposition. The distance L is selected so as to be equal to or greaterthan a radius BR of the bean spot of the read beam LB_(B) (or the readbeam LB_(A) or the read beam LB_(C)), that is to say, BR≦L. The trackpitch width is approximately equal to the radius of the spot of the readbeam.

Similarly, the recording track TR₃ is provided with a tracking pit TR₃located at a position which is further away from the center of thetracking pit TP₁ by a distance 2L (equal to twice the length L) in thecircular direction of the optical disk DK. The sampling timing is timeT₃ at the above position. The recording track TR₄ is provided with atracking pit TR₄ located at a position which is further away from thecenter of the tracking pit TP₁ by a distance 3L in the circulardirection of the optical disk DK. The sampling timing for the aboveposition is time T₄.

Further, each of the other track groups (. . . , TG_(n-1), TG_(n+1),TG_(n+2), . . . ) is provided with the same tracking pit arrangement asthe recording track group TG_(n).

A description will now be given, with reference to FIG. 6, of the mutualrelationship of the read beam projecting positions.

The three read beams LB_(A), LB_(B) and LB_(C) are arranged so as to bespaced apart from each other (offset) in the circular direction of theoptical disk DK by a beam-center-to-beam-center position d, so that thethree read beams can be separated from each other on not-shownphotodetectors. Such an offset arrangement of the read beams is due tothe fact that the radius of the spots of the read beams LB_(A), LB_(B)and LB_(C) are approximately equal to the track pitch, so that, if theread beams LB_(A), LB_(B) and LB_(C) are arranged in a line in theradial direction of the optical disk DK, these beams will overlap andwill not be able to be separated from each other on the photodetectors.Due to the above-mentioned offset arrangement, output signals derivedfrom the three read beams LB_(A), LB_(B) and LB_(C) have a delay T_(d)of time described by the following equation:

    T.sub.d =d/V.sub.c

where V_(C) denotes a linear velocity of the center of the read beamwith respect to the optical disk DK.

With the above in mind, it is necessary to simultaneously output theabove output signals respectively corresponding to the read beamsLB_(A), LB_(B) and LB_(C) and to thereby process the output signals asif the read signals from positions substantially located in the sameradial direction were simultaneously processed. Read timings of thephotodetectors related to the read beams LB_(A), LB_(B) and LB_(C) arecontrolled by performing a correction operation with a delay time T_(d),on a synchronizing clock used for the output signal of the not-shownphotodetector relating to the read beam LB_(B). In the above manner, thedelay time T_(d) can be compensated for, when the delay time T_(d) isequal to an integer multiple of the cycle of the synchronizing clockused for the output signal of the not-shown photodetector associatedwith the read beam LB_(B).

It is also possible to employ the above-mentioned offset arrangementwith respect to pits for tracking. More particularly, the recordingposition of the clock pit CP is used as the reference position, and thetracking pits are arranged at positions which are offset by a time equalto an integer multiple of the period of the clock for synchronization.The read timings at which the clock pits are read by the respective readbeams LB_(A), LB_(B) and LB_(C) with respect to the clock pits CP areused as reference timings, and are generated at times corresponding toan integer multiple of the period of the clock for synchronization.

A description will now be given, with reference to FIG. 7, of anessential part of the reproducing apparatus to generate a tracking errorsignal.

The reproducing apparatus 10 is made up of a crosstalk canceller 11, adecoder 12, a PLL circuit 13, a timing control circuit 14, a firstsample and hold circuit 15, a second sample and hold circuit 16, a thirdsample and hold circuit 17, a sampling timing selecting circuit 18, afirst selecting circuit 19, a second selecting circuit 20 and asubtracter 21.

The crosstalk canceller 11 cancels crosstalk Components from reproducedsignals A, B and C (RF signals) respectively derived from the three readbeams LB_(A), LB_(B) and LB_(C) on the basis of a clock signal CLK inputto the crosstalk canceller 11, and hence output a reproduced signalS_(PB). The decoder 12 decodes the reproduced signal S_(PB) and henceoutputs reproduced data D_(PB). The PLL circuit 13 generates the clocksignal CLK on the basis of the reproduced signal B derived from the readbeam LB_(B) that is the main beam. The timing control circuit 14 outputsa sampling timing signal SMP on the basis of the clock signal CLK. Thefirst sample and hold circuit 15 samples the reproduced signal B at therespective sampling timings T₁ to T₄ on the basis of the sampling timingsignal SMP, and holds sampled components of the reproduced signal B,that is, sampled signals B₁ to B₄ to output them. The second sample andhold circuit 16 samples the reproduced signal A at the respectivesampling timings T₁ to T₄ on the basis of the sampling timing signalSMP, and holds sampled components of the reproduced signal B, that is,sampled signals A₁ to A₄ to output them. The third sample and holdcircuit 17 samples the reproduced signal C at the respective samplingtimings T₁ to T₄ on the basis of the sampling timing signal SMP, andholds sampled components of the reproduced signal C, that is, sampledsignals C₁ to C₄ to output them. The sampling timing selecting circuit18 outputs a sampling timing selecting signal SEL on the basis of thesampled signals B₁ to B₄ and a control signal from a not-showncontroller. The first selecting circuit 19 selects one of the sampledsignals A₁ to A₄ on the basis of the sampling timing selecting signalSEL. The second selecting circuit 20 selects one of the sampled signalsC₁ to C₄ on the basis of the sampling timing selecting signal SEL. Thesubtracter 21 calculates the difference between the sampled signal fromthe first selecting circuit 19 and the sampled signal from the secondselecting circuit 20, and outputs the difference as a tracking errorsignal TE.

A description will now be given, with reference to FIG. 8, of the sampleand hold circuits 15 to 17.

The first sample and hold circuit 15, the second sample and hold circuit16 and the third sample and hold circuit 17 have the same structure aseach other. Each of the circuits 15 to 17 is made up of a first sampleand hold part SH₁, a second sample and hold part SH₂, a third sample andhold part SH.sub., and a fourth sample and hold part SH₄. The firstsample and hold part SH₁ samples and holds the input reproduced signal(A, B or C) at the sampling timing T₁ based on the sampling timingsignal SMP. The second sample and hold part SH₂ samples and holds theinput reproduced signal (A, B or C) at the sampling timing T₂ based onthe sampling timing signal SMP. The third sample and hold part SH₃samples and holds the input reproduced signal (A, B or C) at thesampling timing T₃ based on the sampling timing signal SMP. The fourthsample and hold part SH₄ samples and holds the input reproduced signal(A, B or C) at the sampling timing T₄ based on the sampling timingsignal SMP.

A description will now be given, with reference to FIGS. 9A, 9B, 10A,10B and 11, of a tracking error signal generating operations. In thefollowing description, as shown in FIG. 9A, the read beam LB_(B) tracesthe recording track TR₁.

i) Case where the read beam is located on the center line of therecording track TR₁ (on-track state):

Each of the reproduced signals A, B and C are sampled at timingscorresponding to the recording positions TP_(m) (m=1 to 4) insynchronism with the sampling timing signal SMP. More concretely, thereproduced signal A is sampled at the sampling timings T₁, . . . , T₄ bymeans of the second sample and hold circuit 16. Similarly, thereproduced signal B is sampled at the sampling timings T₁, . . . , T₄ bymeans of the first sample and hold circuit 15 before the clock pit CP isdetected by the read beam LB_(B). The reproduced signal C is sampled atthe sampling timings T₁, . . . , T₄ by means of the third sample andhold circuit 17 before the clock pit CP is detected by the read beamLB_(C). Hence, 12 (=3×4) pieces of sampled data are obtained in theabove-mentioned case.

The waveforms of the reproduced signals A, B and C before and aftersampling are shown in FIG. 9B. In the reproduced signal A, since thetrack pitch is narrow, the tracking pit located on the neighboringrecording track is detected. Hence, the sampled reproduced signal A hassignal components corresponding to not only the tracking pit TP₂ butalso the tracking pits TP₃ and the tracking pit TP₁. In this case, whenthe levels (degree of darkness of the dark portion) of the sampledsignals are compared with each other, the following will be seen. Thatis, the sampled signal (sampled at sampling timing T₂) has the greatestpeak (darkest). The levels of the sampled signals corresponding to thetracking pits TP₃ and TP₁, which are approximately equal to each other,are less than the level of the sampled signal derived from the trackingpit TP₂. The peak of the reproduced signal A derived from the trackingpit TP₄ is the smallest.

When the levels of the sampled signals of the reproduced signal B arecompared with each other, the following will be seen. That is, thesampled signal (sampled at sampling timing T₁) has the greatest peak(darkest). The levels of the sampled signals corresponding to thetracking pits TP₄ and TP₂, which are approximately equal to each other,are less than the level of the sampled signal derived from the trackingpit TP₁. The peak of the reproduced signal A derived from the trackingpit TP₃ is the smallest.

When the levels of the sampled signals of the reproduced signal C arecompared with each other, the following will be seen. That is, thesampled signal (sampled at sampling timing T₄) has the greatest peak(darkest). The levels of the Sampled signals corresponding to thetracking pits TP₃ and TP₁, which are approximately equal to each other,are less than the level of the sampled signal derived from the trackingpit TP₄. The peak of the reproduced signal A derived from the trackingpit TP₂ is the smallest.

Next, the sampling timing selecting circuit 18 compares the four sampledvalues of the reproduced signal B (more particularly, sampled signals B₁to B₄ : see FIG. 9B) derived from the read beam LB_(B) that is the mainbeam with each other, and identifies the tracking pit on the recordingtrack which is being traced by the read beam LB_(B). In the above case,the reading peak of the tracking pit TP₁ is the greatest peak, and hencethe tracking pit on the recording track TR₄ traced by the read beamLB_(B) is identified as the tracking pit TP₁.

Subsequently, the sampling timing selecting circuit 18 provides thefirst selecting circuit 19 and the second selecting circuit 20 with thesampling timing selecting signal SEL used to select the sampled signalsampled at the same sampling timing as the sampling timing T₁ of thetracking pit TP₁ that is the tracking pit on the recording track tracedby the read beam LB_(B).

As a result, the first selecting circuit 19 selects the sampled signalA₁, and the second selecting circuit 20 selects the sampled signal C₁.These selected signals are output to the subtracter 21. The subtracter21 Generates the tracking error Signal TE by using the followingequation (1) and outputs it:

    TE=A.sub.1 -C.sub.1.

In this case, if the read beam LB_(B) is located on the recording trackTR_(m) (on-track state), the read peak of the sampled signal A₁ and theread peak of the sampled signal C₁ are equal to each other, and thetracking error TE is equal to 0.

A description will now be given of an operation in which the read beamLB_(B) is off the center line of the recording track.

ii) Case where the read beam LB_(B) is off towards the recording trackTR₂ :

FIG. 10A shows waveforms of the reproduced signals A and C observed whenthe read beam LB_(B) is off towards the recording track TR₂. FIG. 10Adiffers from FIG. 9B in that the condition where the correctionoperation for compensating for the delay time T_(d) has been performed,is shown.

As compared to the on-track state (see FIG. 9B), the sampled signal A₁of the reproduced signal A has a small read peak, while the sampledsignal C₁ of the sampled signal C has a large read peak (see FIG. 9B).Hence, the tracking error signal TE is written as follows:

    TE=A.sub.1 -C.sub.1 <0

Hence, it is possible to detect a deviation of the read beam LB_(B)towards the recording track TR₂ and the degree of such a deviation.

iii) Case where the read beam LB_(B) is off towards a recording trackTR₄ ':

FIG. 10B shows waveforms of the reproduced signals A and C observed whenthe read beam LB_(B) is off towards the recording track TR₄ ' in whichthe condition where the correction operation for compensating for thedelay time T_(d) has been performed, is shown.

As compared to the on-track state (see FIG. 9B), the sampled signal A₁of the reproduced signal A has a large read peak, while the sampledsignal C₁ of the reproduced signal C has a small peak (see FIG. 9B).Hence, the tracking error signal TE is written as follows:

    TE=A.sub.1 -C.sub.1 >0

Hence, it is possible to detect a deviation of the read beam LB_(B)towards the recording track TR₄ ' and the degree of such a deviation.

FIG. 11 shows concrete examples of the tracking error signal TE. Asshown in FIG. 11, the tracking error signal TE is a signal obtained bycombining the first through fourth tracking error signals TE₁ to TE₄obtained at the sampling timings T₁ to T₄ together. More concretely,when data is reproduced from the recording track assigned track numberTNO=1, the first tracking signal TE₁ (=A₁ -C₁) is used as the trackingerror signal TE. When data is reproduced from the recording trackassigned track number TNO=2, the second tracking signal TE₂ (=A₂ -C₂) isused as the tracking error signal TE. When data is reproduced from therecording track assigned track number TNO=3, the third tracking signalTE₃ (=A₃ -C₃) is used as the tracking error signal TE. When data isreproduced from the recording track assigned track number TNO=4, thefourth tracking signal TE₄ (=A₄ -C₄) is used as the tracking errorsignal TE. FIG. 11 integrally illustrates the above tracking errorsignals TE₁ to TE₄.

As has been described above, according to the first embodiment of thepresent invention, there is only one tracking pit every four tracks at asampling timing even in the case where the track pitch is diminished inorder to improve the recording density. Hence, there is no influence ofthe neighboring tracks, and it is possible to easily and certainlygenerate the tracking error signal by means of the three beam method byusing three read beams each having the same size as that of the readbeams which are conventionally used. Further, it is possible to simplifythe structure of the recording apparatus because it is not necessary toprovide any wobble pits.

One Modification of the First Embodiment

In the first embodiment of the present invention, by performing thetracking servo by use of one of the first through fourth tracking errorsignals TE₁ to TE₄ shown in FIG. 11, that is, by performing the trackingservo by use of a constant sampling timing, the recording track to bepulled in, becomes different depending upon the constant samplingtiming. Using the above, it is possible to perform a track jumpoperation. A further description will now be given of a case in whichthe read beam LB_(B) that is the main beam is jumped from the recordingtrack TR₂ to the recording track TR₄ (see FIG. 5). First of all, thetracking error signal TE₃ is generated at the sampling timing T₃corresponding to the recording track TR₃ adjacent, in the direction ofthe jump, to the recording track TR₂, which is being read by the readbeam LB_(B). Immediately before pulling it in the recording track TR₃,the tracking signal TE₄ is generated at a sampling timing correspondingto the recording track TR₄ adjacent, in the jump direction, to therecording track TR₃ so as to pull it in the recording track TR₄. Bysequentially switching the sampling timings in the above manner, itbecomes possible to easily perform the track jump control.

Another Modification of the First Embodiment

In the case where the tracking pits are arranged according to the firstembodiment of the present invention, by paying attention to the samplingtiming of a tracking pit, it is possible to count the number ofrecording tracks crossed in the track jump operation, by a unit of fourrecording tracks. For example, if the sampling timing of interest is thesampling timing T₁ for the tracking pit TP₁, the recording track (TR₁)synchronized with the sampling timing T₁ appears every four recordingtracks. Hence, it is possible to count the number of recording tracksevery four recording tracks. In this case, three recording tracks orless can be counted by checking the positions of the tracking pits.

Second Embodiment

The description has been given of the operation of the first embodimentafter pulling the read beam in a recording track. The trackingcontrollable range is approximately equal to 1/2 of the track pitch (P)when the tracking error signal TE (see FIG. 11) generated in the firstembodiment is used to pull the read beam in a recording track.

Meanwhile, the tracking pull-in possible range is approximately equal toone track pitch (P) by fixing the sampling timing as shown in FIG. 11.Hence, the read beam can be more easily pulled in a recording track bymeans of the constant sampling timing, as compared with the firstembodiment.

With the above in mind, the tracking error signals (TE₁, . . . , TE₄)are generated at the constant sampling timing when the read beam ispulled in. After the read beam has been pulled in, the sampling timingsare switched and the tracking servo is performed by using the normaltracking error signals. In this manner, the read beam can be more stablypulled in. The above method is particularly effective to a high-speedsearching operation.

Third Embodiment

The sampling timing signal applied to the second sample and hold circuit16 and the third sample and hold circuit 17 is generated by a set of PLLcircuit and timing control circuit commonly used for these circuits 16and 17. In the third embodiment, sampling timing signals are generatedfor the respective sample and hold circuits.

FIG. 12 is a block diagram of a reproducing apparatus 40 according tothe third embodiment. In FIG. 12, parts that are the same as parts usedin the first embodiment shown in FIG. 7 are given the same referencenumbers, and a detailed description thereof will be omitted. The thirdembodiment differs from the first embodiment in that the thirdembodiment includes a PLL circuit 13_(A), a timing control circuit14_(A), a PLL circuit 13_(C) and a timing control circuit 14_(C). ThePLL circuit 13_(A) generates a clock signal on the basis of thereproduced signal A and outputs the clock signal. The timing controlcircuit 14_(A) outputs a sampling timing signal SMPA applied to thesecond sample and hold circuit 16 on the basis of the clock signalgenerated by the. PLL circuit 13_(A). The PLL circuit 13_(C) generates aclock signal on the basis of the reproduced signal C. The timing controlcircuit 14_(C) outputs a sampling timing signal SMPC applied to thethird sample and hold circuit 17 on the basis of the clock signalgenerated by the PLL circuit 13_(C).

As a result, the second sample and hold circuit 16 and the third sampleand hold circuit 17 performs the sample and hold operations with therespective timings. Hence, it is possible to prevent a deviation betweenthe reading position defined by the sampling timing based on thesampling signal SMP and the actual recording position of the trackingpit and to obtain the more accurate tracking error signal TE, such adeviation being caused by fluctuation in rotation of the optical disk.

Fourth Embodiment

The fourth embodiment uses the optical disk used in the firstembodiment, and is adapted such that the tracking signal is generated inthe same manner as the conventional sampled servo method, by regardingthe tracking pits formed on the respective recording tracks as wobblepits of an optical disk of the conventional sampled servo method. Inthis case, the fourth embodiment differs from the conventional sampledservo manner in that the positions of the wobble pits (equivalent to thetracking pits) are different from each other for each recording track tobe traced, and the sampling timing is switched every recording track.

A description will now be given of an essential part of a reproducingapparatus 50 according to the fourth embodiment of the presentinvention, with reference to FIG. 13.

The reproduced apparatus 50 is made up of the crosstalk canceller 11,the decoder 12, the PLL circuit 13, the timing control circuit 14, afirst sample and hold part SH₁₁, a second sample and hold part SH₁₂, athird sample and hold part SH₁₃, a fourth sample and hold part SH₁₄, atiming selecting circuit 34, a first selecting circuit 31, a secondselecting circuit 32, and a subtracter 33.

The crosstalk canceller 11 cancels crosstalk components from reproducedsignals A, B and C (RF signals) respectively derived from the three readbeams LB_(A), LB_(B) and LB_(C) on the basis of the clock signal CLKinput to the crosstalk canceller 11, to output the reproduced signalS_(PB). The decoder 12 decodes the reproduced signal S_(PB) and henceoutputs reproduced data D_(PB). The PLL circuit 13 generates the clocksignal CLK on the basis of the reproduced signal B derived from the readbeam LB_(B) that is the main beam. The timing control circuit 14 outputsthe sampling timing signal SMP on the basis of the clock signal CLK. Thefirst sample and hold circuit SH₁₁ samples the reproduced signal B atthe sampling timing T₁ on the basis of the sampling timing signal SMP,and holds a sampled signal B₁ of the reproduced signal B. The secondsample and hold circuit SH₁₂ samples the reproduced signal B at thesampling timing T₂ on the basis of the sampling timing signal SMP, andholds a sampled signal B₂ of the reproduced signal B. The third sampleand hold circuit SH₁₃ samples the reproduced signal B at the samplingtiming T₃ on the basis of the sampling timing signal SMP, and holds asampled signal B₃ of the reproduced signal B. The fourth sample and holdcircuit SH₁₄ samples the reproduced signal B at the sampling timing T₄on the basis of the sampling timing signal SMP, and holds a sampledsignal B₄ of the reproduced signal B. The sampling timing selectingcircuit 34 outputs a sampling timing selecting signal TSEL on the basisof the sampled signals B₁ to B₄ and a control signal from the controller30. The first selecting circuit 31 selects one of the sampled signals B₁to B₄ on the basis of the sampling timing selecting signal TSEL. Thesecond selecting circuit 32 selects one of the sampled signals B₁ to B₄other than the sampled signal selected by the first selecting circuit31, on the basis of the sampling timing selecting signal TSEL. Thesubtracter 33 calculates the difference between the sampled signal fromthe first selecting circuit 31 and the sampled signal from the secondselecting circuit 32, and outputs the difference as a tracking errorsignal TE.

A description will now be given of the operation of the fourthembodiment of the present invention.

Firsts regarding the reproduced signal B, the sampling is carried out attimings corresponding to the position of recording of the tracking pitsTP_(m) (m=1 to 4) on the basis of the sampling timing signal SMP. Moreconcretely, when the timing control circuit 14 outputs the samplingtiming signal SMP on the basis of the clock signal CLK, the first sampleand hold part SH₁₁ samples and holds the input reproduced signal B atthe sampling timing T₁, and outputs the sampled signal B₁. Similarly,the second sample and hold part SH₁₂ samples and holds the inputreproduced signal B at the sampling timing T₂ on the basis of thesampling timing signal SMP, and outputs the sampled signal B₂. The thirdsample and hold part SH₁₃ samples and holds the input reproduced signalB at the sampling timing T₃, and outputs the sampled signal B₃. Thefourth sample and hold part SH₁₄ samples and holds the input reproducedsignal B at the sampling timing T₄ on the basis of the sampling timingsignal SMP, and outputs the sampled signal B₄.

Subsequently, the sampling timing selecting circuit 34 compares thesampled signals B₁ to B₄, and identifies the timing of the tracking pitformed on the recording track being reproduced. That is, the sampledsignal having the greatest level (darkness) is identified as timing ofthe tracking pit. More concretely, in a case as shown in FIG. 14A, thesampling timing T₂ is selected as timing of the tracking pit TP₂.

Then, two sampling signals are selected in order to obtain the trackingerror signal TE from the selected sampling timing. More specifically, onthe basis of the selected sampling timing T₂, the timing selectingsignal TSEL is output to the first selecting circuit 31 and the secondselecting circuit 32 on the basis of a conversion table (see FIG. 15)stored beforehand. As a result, the sampled signal B₁ is selected andoutput by the first selecting circuit 31, and the sampled signal B₃ isselected and output by the second selecting circuit 32.

Similarly, when the sampling timing T₁ is selected, the sampled signalB₄ is selected and output by the first selecting circuit 31, and thesampled signal B₂ is selected by the second selecting circuit 32. Whenthe sampling timing T₃ is selected, the sampled timing B₂ is selectedand output by the first selecting circuit 31, and the sampled signal B₄is selected and output by the second selecting circuit 32. When thesampling timing T₄ is selected, the sampled signal B₃ is selected andoutput by the first selecting circuit 31, and the sampled signal B₁ isselected and output by the second selecting circuit 32.

Hence, the subtracter 21 generates the tracking error signal TE in thefollowing equation using the two sampled signals selected by the firstselecting circuit 31 and the second selecting circuit 32:

TE=(output of 1st selecting circuit 31)-(output of 2nd selecting circuit32)

Thus, in a case where the light beam LB_(B) is located on the recordingtrack TR₂ being traced, as shown in FIG. 14A, the levels of the sampledsignals respectively selected by the first selecting circuit 31 and thesecond selecting circuit 32 are equal to each other, as indicated bysampled signals B₁ and B₃ of the reproduced signal shown in FIG. 14B,and the tracking error signal TE (=B₁ -B₃) becomes equal to zero.

Next, a description will now be given of operation in the case where thelight beam LB_(B) deviates from the center line of the recording trackTR₂.

i) Case where the light beam LB_(B) is off towards the recording trackTR₃ :

FIG. 14C shows a waveform of the reproduced signal B (illustrated in atime sequence) observed when the light beam LB_(B) is off towards therecording track TR₃. As compared to the on-track state (see FIG. 14B),the sampled signal B₁ of the reproduced signal B corresponding to thetracking pit TP₁ has a small read peak, while the sampled signal B₃ ofthe sampled signal B corresponding to the tracking pit TP₃, has a largeread peak (see FIG. 14B). Hence, the tracking error signal TE is writtenas follows:

    TE=B.sub. -B.sub.3 <0

Hence, it is possible to detect a deviation of the read beam LB_(B)towards the recording track TR₃ and the degree of such a deviation.

ii) Case where the read beam LB_(B) is off towards recording track TR₁ :

FIG. 14D shows waveforms of the reproduced signal B observed when theread beam LB_(B) is off towards the recording track TR₁. As compared tothe on-track state (see FIG. 14B), the sampled signal B₁ of thereproduced signal B corresponding to the tracking pit TP₁ has a largeread peak, while the sampled signal B₃ of the reproduced signal Bcorresponding to the tracking pit TP₃, has a small peak (see FIG. 14B),Hence, the tracking error signal TE is written as follows:

    TE=B.sub.1 -B.sub.3 >0

Hence, it is possible to detect a deviation of the read beam LB_(B)towards the recording track TR₁ and the degree of such a deviation.

iii) Case where the light beam LB_(B) is on the recording track TR₁ :

A waveform (illustrated in a time sequence) of the reproduced signalobserved when the light beam LB_(B) on the recording track TR₁, is shownin FIG. 14E for reference. In this case, the read peak B₁ of thereproduced signal B corresponding to the tracking pit TP₁ is thegreatest among the peaks B₁ to B₄, and the levels of the peaks B₂ and B₄respectively corresponding to the tracking pits TP₁ and TP₄ are equal toeach other. Hence, the tracking error signal TE is as follows:

    TE=B.sub.2 -B.sub.4 =0

In this manner, it is possible to detect the light beam LB_(B) locatedon the recordin₉ track TR₁.

As has been described above, according to the fourth embodiment, thereis only one tracking pit every four tracks at a sampling timing even inthe case where the track pitch is diminished in order to improve therecording density. Hence, there is no influence of the neighboringtracks, and it is possible to easily and certainly generate the trackingerror signal by using three read beams each having the same size as thatof the read beams which are conventionally used. Further, it is possibleto simplify the structure of the recording apparatus because thetracking pits can be used in place of wobble pits and new wobble pitsare not needed.

In the aforementioned embodiments of the present invention, the numberof recording tracks corresponding to the period of the recordingpositions of tracking pits is equal to four. However, the presentinvention can be applied to optical disks in which the number ofrecording tracks corresponding to the cycle of the recording positionsof tracking pits is equal to three or more.

According to the present invention, it is not necessary to form highlyprecise wobble pits on optical disks and it is hence possible tosimplify the recording apparatus and easily record information on tracksarranged with a reduced track pitch.

It is also possible to record information with a high density and toeasily and certainly generate the tracking error signal even for areduced track pitch. It is also possible to increase the controllablepull-in range using the tracking error signal even for a reduced trackpitch and to stably pull the read beam in a track.

It is also possible to count the number of recording tracks even whentracks are crossed at high speed because the count operation isperformed by a unit of cycle of the recording positions of trackingpits.

The invention may be embodied in other specific forms without departingfrom the spirit of essential characteristics thereof. The presentembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

What is claimed is:
 1. A tracking error signal generating apparatus inan optical disc player, which generates main read beam for reading datarecorded on one of tracks formed on an optical disk, and two sub readbeams for reading data recorded on two tracks adjacent to said one ofthe tracks,said optical disk comprising: a plurality of recordingtracks, each of the recording tracks having a data area for storingdata, and a servo control information area for storing servoinformation; and tracking pits respectively formed on n neighboringrecording tracks, which are adjacent to each other in a radial directionof the optical disk, where n is an integer not less than 3, saidtracking pits being located in the servo control information area ofeach of said n neighboring recording tracks and being spaced apart fromeach other by a distance not less than a radius of a beam spot of theread beams, said tracking pits of said n neighboring recording tracksbeing located on different radial lines of the optical disk, saidtracking error signal generating apparatus comprising:timing generatingmeans for generating a plurality of sampling timings respectivelycorresponding to recording positions of the tracking pits for the mainread beam and the two sub read beams; sample and hold means for samplingreproduced signals respectively corresponding to the main read beam andthe two sub read beams on the basis of the plurality of sampling timingsand for holding the sampled reproduced signals; comparing means forcomparing levels of the sampled reproduced signals respectivelycorresponding to the plurality of sampling timings and for outputting aselecting signal indicating one of the sampling timings at which one ofthe sampled reproduced signals has a largest level; selecting means forselectively outputting, from said sample and hold means, the sampledreproduced signals obtained from the two sub read beams at said one ofthe sampling timings indicated by said selecting signal; and operationmeans for outputting a tracking error signal on the basis of the sampledreproduced signals from said selecting means.
 2. A tracking controlapparatus having a tracking error signal generating apparatus in anoptical disc player, which generates main read beam for reading datarecorded on one of tracks formed on an optical disk, and two sub readbeams for reading data recorded on two tracks adjacent to said one ofthe tracks,said optical disk comprising: a plurality of recordingtracks, each of the recording tracks having a data area for storingdata, and a servo control information area for storing servoinformation; and tracking pits respectively formed on n neighboringrecording tracks, which are adjacent to each other in a radial directionof the optical disk, where n is an integer not less than 3, saidtracking pits being located in the servo control information area ofeach of said n neighboring recording tracks and being spaced apart fromeach other by a distance not less than a radius of a beam spot of theread beams, said tracking pits of said n neighboring recording tracksbeing located on different radial lines of the optical disk, saidtracking error signal generating apparatus comprising:timing generatingmeans for generating a plurality of sampling timings respectivelycorresponding to recording positions of the tracking pits for the mainread beam and the two sub read beams; sample and hold means for samplingreproduced signals respectively corresponding to the main read beam andthe two sub read beams on the basis of the plurality of sampling timingsand for holding the sampled reproduced signals; comparing means forcomparing levels of the sampled reproduced signals respectivelycorresponding to the plurality of sampling timings and for outputting aselecting signal indicating one of the sampling timings at which one ofthe sampled reproduced signals has a largest level; selecting means forselectively outputting, from said sample and hold means, the sampledreproduced signals obtained from the two sub read beams at said one ofthe sampling timings indicated by said selecting signal; and operationmeans for outputting a tracking error signal on the basis of the sampledreproduced signals from said selecting means, said tracking controlapparatus comprising:signal generating means for generating a pull-intracking error signal from read signals of the tracking pits read by thetwo sub read beams at one of the sampling timings; and pull-in means forpulling the main read beam in one of the recording tracks on the basisof the pull-in tracking error signal.
 3. A tracking control apparatushaving a tracking error signal generating apparatus in an optical discplayer, which generates main read beam for reading data recorded on oneof tracks formed on an optical disk, and two sub read beams for readingdata recorded on two tracks adjacent to said one of the tracks,saidoptical disk comprising: a plurality of recording tracks, each of therecording tracks having a data area for storing data, and a servocontrol information area for storing servo information; and trackingpits respectively formed on n neighboring recording tracks, which areadjacent to each other in a radial direction of the optical disk, wheren is an integer not less than 3, said tracking pits being located in theservo control information area of each of said n neighboring recordingtracks and being spaced apart from each other by a distance not lessthan a radius of a beam spot of the read beams, said tracking pits ofsaid n neighboring recording tracks being located on different radiallines of the optical disk, said tracking error signal generatingapparatus comprising:timing generating means for generating a pluralityof sampling timings respectively corresponding to recording positions ofthe tracking pits for the main read beam and the two sub read beams;sample and hold means for sampling reproduced signals respectivelycorresponding to the main read beam and the two sub read beams on thebasis of the plurality of sampling timings and for holding the sampledreproduced signals; comparing means for comparing levels of the sampledreproduced signals respectively corresponding to the plurality ofsampling timings and for outputting a selecting signal indicating one ofthe sampling timings at which one of the sampled reproduced signals hasa largest level; selecting means for selectively outputting, from saidsample and hold means, the sampled reproduced signals obtained from thetwo sub read beams at said one of the sampling timings indicated by saidselecting signal; and operation means for outputting a tracking errorsignal on the basis of the sampled reproduced signals from saidselecting means, said tracking control apparatus comprising:signalgenerating means for comparing levels of the read signals of the mainread beam, at respective read timings of the tracking pits formed on theadjacent recording tracks, with each other, selecting the read timing atwhich the level of read signal is larger, and generating a pull-intracking error signal from the read signals of the two sub read beams atthe selected read timing; and pull-in means for pulling the main readbeam in one of the recording tracks on the basis of the pull-in trackingerror signal.
 4. A tracking error signal generating apparatus forgenerating a tracking error signal from read signals from an opticaldisk,said optical disk comprising: a plurality of recording tracks, eachof the recording tracks having a data area for storing data, and a servocontrol information area for storing servo information; and trackingpits respectively formed on n neighboring recording tracks, which areadjacent to each other in a radial direction of the optical disk, wheren is an integer not less than 3, said tracking pits being located in theservo control information area of each of said n neighboring recordingtracks and being spaced apart from each other by a distance not lessthan a radius of a beam spot for reading data from the optical disk,said tracking pits of said n neighboring recording tracks being locatedon different radial lines of the optical disk, said tracking errorsignal generating apparatus comprising:read means for outputting readsignals at a plurality of read timings corresponding to recordingpositions of the tracking pits by reading a recording track of interestby means of a read beam; comparing means for comparing levels of theread signals respectively obtained at the read timings and for selectingone of the plurality of read timings at which one of the read signalshas a largest level; and operation means for selecting read timings atwhich the tracking pits formed on the recording tracks adjacent to saidrecording track of interest are read on the basis of the selected readtimings selected by the comparing means and for generating the trackingerror signal on the basis of the read signals corresponding to theselected read timings.